The welcome email sends before the trigger. You need to use the trigger onBeforeUserApproval so the data is up to date before the email fires.

That's not the Welcome email. That's the Pending email, which is fired well before the Approval trigger and Welcome email. The welcome email can be delayed. The Pending email is always sent immediately after registration. Please try using the triggers onAfterUserRegistration (frontend) and onAfterNewUser (backend). Should always be done immediately after registration especially given you're restructuring the username.

The onBeforeUserApproval is the appropriate trigger and it is fired before the email. It's likely your conditional or your query is failing all together and the trigger isn't the problem as you have the correct trigger. Please test your query without the Conditional then also test a more basic query as well as test queries in database directly with test date to confirm they work.

You're welcome to also try onUserActive or onBeforeUserActive triggers, but they fire directly inside the activation function and directly before the emails send which this could cause it to trigger on welcome and pending emails alike. This is simply a trial and error process. Please see tutorials within my signature regarding "event triggers" for available triggers.